Various tradeoffs exist in the design of radiation sensors. Some of the desirable attributes of a radiation sensor that are affected by tradeoffs include cost, sensitivity, spectral discrimination, discrimination of one particle type from another, spatial discrimination or imaging ability, particle tracking, and energy consumption. Although radiation sensors have been in development for many years, there remains a need for new designs that achieve favorable tradeoffs among these and other attributes. Two rapidly developing fields that have greatly increased the demand for new sensor designs are radiological surveillance and radiological medicine.
One recent design approach, motivated in particular by the need for new sensors for radiological surveillance, is described in our U.S. patent application Ser. No. 13/559,370, cited above. Embodiments described there are neutron detectors using, e.g., helium-3 as a sensing medium. Features are described that improve the rejection of gamma-ray-induced background noise, reduce the total helium-3 requirement, and provide for increased spatial resolution and directional discrimination.
One of the embodiments we described was a thermal neutron detector in which a high pressure ion chamber was formed in a dielectric material. First and second electrodes were formed in the high pressure ion chamber, which was filled with a neutron absorbing material to chamber pressures up to several hundred atm. and was surrounded at least in part by a neutron moderating material. The high pressure ion chamber had a pair of parallel, substantially planar surfaces on which respective first and second electrodes were formed.
Another of the embodiments we described was a neutron detector with monolithically integrated readout circuitry. In that embodiment, the ion chamber was formed in a bonded semiconductor die that included an etched semiconductor substrate bonded to an active semiconductor substrate. The first and second electrodes were formed in the ion chamber and were electrically coupled to readout circuitry formed in a portion of the active semiconductor substrate.
Although useful, the above-described design approach still leaves room for extensions, e.g. for alpha, beta, and gamma particle detection, and for competing approaches that may provide further capabilities or that may be more optimal for certain applications.